We thank the fishermen who collected the scales and phenotypic information and the people who organized and read the scales, in particular J. Kuusela and J. Haantie, as well as J.-P. Pohjola for reading the sonar data and M Länsman for compiling detailed river catch and effort data. A. Holmberg and NA Holmberg are thanked for sharing their extensive knowledge of traditional Sami fishing practices. We also thank E. Eriksen for providing corrected data on krill biomass and Ø. Langangen for sharing codes and information on the Gompertz multi-species model. Four anonymous reviewers are thanked for their constructive comments on earlier versions. Funding: This project has received funding from the Academy of Finland (projects no. 284941, 286334, 314254, 314255, 327255 and 325964) as well as the European Research Council (ERC) under the Research and Innovation Program European Union Horizon 2020 (grant agreement no. 742312). Part of YC’s salary was funded by the Research Council of Norway (projects no. 275862 EcoEvoGene and 280308 SeaSalar). YC is also affiliated with the Center for Biodiversity Dynamics (CBD, NTNU) Author’s contributions: JE and PO coordinated collection of scale samples and river fishing data; CRP, YC, TA and JE designed the study; YC did the lab work and analyzed the data; YC, CRP and TA wrote the manuscript and all authors contributed to its revision. Competing interests: The authors declare an absence of competing financial interests. Availability of data and materials: Datasets generated for the current study and custom codes are available in a public data repository that becomes accessible upon release (24). All other data necessary to evaluate the conclusions of the article are present in the article or the supplementary documents.